The present invention concerns a magnetic field sensor, and in particular a magnetic field sensor that can be manufactured using the technology of surface micromechanics.
Although applicable to any magnetic field sensor, the present invention and the problem on which it is based are explained with reference to a magnetic field sensor that can be manufactured using the technology surface micromechanics, for use in automotive engineering.
Magnetic field sensors can be used in many ways in automotive engineering, for example in antilock braking systems (ABS) or in automatic slip control (ASR) systems as wheel sensors, as position sensors for needle valves or ignition pulse generators, as steering wheel angle transducers, as crankshaft position transducers, etc. The demands placed on these magnetic field sensors in terms of mechanical strength, e.g. shock resistance and temperature resistance, are usually very high.
There exist in the related art a large number of known magnetic field sensors which utilize the applied force of a magnetic field on a conductor through which a current is passing. The best known example thereof is the Hall sensor.
Disadvantages that have emerged with the aforesaid known approaches are that they cannot withstand the severe mechanical and/or thermal stresses, and/or have too little sensitivity, and/or are very costly.
The magnetic field sensor according to the present invention has the advantage, as compared to known approaches to the problem, that it can be designed in such a way that it withstands severe mechanical stresses and exhibits high sensitivity simultaneously with low temperature dependence.
The underlying idea behind the present invention is that a conductor loop whose area is modulated, i.e. that has a definable time dependence, remains at a voltage as long as a magnetic field is not passing through it. As soon as this conductor loop is exposed to a magnetic field, however, the result of the area modulation is that the magnetic flux "PHgr" continually changes, causing a voltage induction that is proportional to the magnetic flux density and to the change in area over time. This voltage is picked off at the ends of the conductor loop and is analyzed in accordance with the mechanical excitation. The magnetic field sensor according to the present invention can be used to sense both constant magnetic fields and alternating magnetic fields, up to a system-related limit frequency.
According to a preferred development, in the undeformed state the conductor loop encloses an area having two longitudinal sides substantially parallel to one another, and the deformation device deforms the two longitudinal sides to change the enclosed area. It is thus advantageously possible to achieve a large change in area.
According to a further preferred development, the deformation device is configured such that it excites the two longitudinal sides to opposite-direction resonant flexural oscillations. It is thus advantageously possible to achieve a particularly large change in area utilizing resonance exaggeration.
According to a further preferred development, the conductor loop is configured such that the opposite-direction resonant flexural oscillations have a different resonant frequency from the corresponding same-direction resonant flexural oscillations. It is thereby advantageously possible to avoid interferences with the undesired same-direction resonant flexural oscillations, in which the net change in area is substantially zero.
According to a further preferred development, the deformation device is configured such that it deforms the deformable segments by way of a capacitive coupling. As a result, neither friction losses nor wear occur during excitation. In addition, capacitive excitation devices of this kind are known from other sectors, for example comb structures of acceleration sensors.
According to a further preferred development, the magnetic field sensor is manufactured using the technology of surface micromechanics, and has a substrate that is preferably made of silicon (or of another electrically conductive material). The conductor loop has substantially a rectangular shape, whose longitudinal sides are arranged floatingly above the substrate and are deformable by the deformation device, and whose widthwise sides are mounted floatingly on the substrate. This particular embodiment by high sensitivity simultaneously with low temperature dependence.
According to a further preferred development, the conductor loop has a continuous, nondeformable first widthwise side having a greater thickness than the longitudinal sides, which is connected, via at least one deformable floating strut having substantially the thickness of the longitudinal sides, to at least one connector pad anchored in the substrate. This rigid first widthwise side stabilizes the width of the surface.
According to a further preferred development, the conductor loop has a split nondeformable second widthwise side having a greater thickness than the longitudinal sides, whose parts is connected via a respective deformnable floating strut, having substantially the thickness of the longitudinal sides, to a respective connector pad anchored in the substrate. This split rigid second widthwise side also stabilizes the width of the surface, and allows the induced voltage to be picked off advantageously.
According to a further preferred development, the longitudinal sides are connected at their first end, via a deformable floating first resilient strut having substantially the thickness of the longitudinal sides, to a connector pad anchored in the substrate. With this embodiment, the split rigid second widthwise side is advantageously omitted, so that the structure becomes simpler.
According to a further preferred development, the longitudinal sides are connected at their second end, via a deformable floating second resilient strut having substantially the thickness of the longitudinal sides, to the continuous nondeformable first widthwise side.
According to a further preferred development, an additional mass is provided floatingly above the substrate in the middle of the deformable longitudinal sides. This additional mass is advantageously used to adjust the resonant frequency.
According to a further preferred development, a comb drive device connected to the longitudinal sides is provided as the deformation device. This connection can be either direct, by the fact that comb teeth are provided on the longitudinal sides; or indirect, by the fact that comb teeth are provided on an additional mass that is possibly present.